They possess whiskers, tribosphenic molars, and a long snout. They have a postorbital bar, but their eye sockets are not yet completely encased in bone. They have flat nails on all digits but for the second digit of each foot, on which they have a toilet claw. They also have large mobile ears.

All but one of the prosimii have wet noses (called a rhinarium). The odd one out is the tarsier. Because of this, some people use the semiordersStrepsirhini (with rhinarium {literally, 'split nose'}) and Haplorhini (no rhinarium). The semiorder Strepsirhini is identical to the Prosimii except for the fact that it leaves out the tarsier.